Memory devices are utilized as non-volatile memory for a wide range of electronic applications in need of high memory densities, high reliability, and data retention without power. Non-volatile memory may be used in, for example, personal computers, portable memory sticks, solid state drives (SSDs), digital cameras, cellular telephones, portable music players such as MP3 players, movie players, and other electronic devices.
Memory devices are typically provided as internal, semiconductor, integrated circuits in computers or other electronic devices. There are many different types of memory, including random-access memory (RAM), read only memory (ROM), dynamic random access memory (DRAM), synchronous dynamic random access memory (SDRAM), flash memory, and resistance memory, among others. Types of resistive memory include phase change random access memory (PCRAM) and resistive random access memory (RRAM), for instance.
Resistive memory devices, such as PCRAM devices, can include a resistive variable material such as a phase change material, for instance, which can be programmed into different resistance states to store data. The particular data stored in a phase change memory cell can be read by sensing the cell's resistance e.g., by sensing current and/or voltage variations based on the resistance of the phase change material.
Some multi-bit phase change memory cells employ a “series resistance” approach, which can require the use of complex program-verify algorithms, for instance. Additionally, such cells may incur resistance drift, in which the resistance of anamorphous state increases over time. Resistance drift can diminish the retention capability of the cell.